A serious problem exists in operating rooms. Specifically, the chemical determination of oxygen level in blood consumes at least 3 to 5 minutes. A patient deprived of blood oxygen for such a duration typically incurs irreversible brain damage if not death.
U.S. Pat. No. 2,706,927 to Wood disclosed the computation of oxygen saturation from measurements of light absorption of body tissue at two wavelengths. A series of devices and procedures have been founded using this technology.
A required peripheral device of such photoelectric oximeters is a photoelectric probe. Typically, such a probe is clamped to an appendage of a patient's body, such as an ear or a finger. Such probes require at least one light source for directing light into the appendage and at least one sensor for receiving light diffused out of the appendage. One method of obtaining light of the desired frequency had been to use a light source of indeterminate wavelength range in combination with a monochromatic filter of known output. Such devices are inefficient, and result in unwanted power demands and heat generation.
U.S. Pat. No. 3,704,706 to Herczfeld et al. disclosed the use of a solid state red laser in an optical probe with a solid state photodetector. Although lasers are useful for emitting monochromatic light of known wavelength, thereby eliminating need for a filter, they remain expensive and unwieldy.
U.S. Pat. No. 3,847,483 to Shaw et al. disclosed the use of light emitting diodes to provide the necessary monochromatic light. The probe of Shaw required expensive fiber optic cables.
A problem with all prior art devices is that they are too expensive to be readily disposable. The need for a truly disposable probe is great, given the many surgical applications in which sterility must be assured. The prior art optical probes, being more or less permanent portions of their respective oximeters, were subjected to a one time determination of the wavelength of the light sources therein and the oximeter was then programmed or adjusted to process light of the known wavelength.
A problem in developing disposable probes, therefore, has been the necessity to avoid having to reprogram or adjust the oximeter for each new probe or alternately to maintain probes within narrow limits of wavelength variation, a clearly impractical task.
Re-calibration, perhaps necessitating return of the oximeters to the factory, can become necessary even for prior art devices when, for example, a probe is broken. Alternatively, a supply of light sources having consistently identical wavelengths is required. In particular, light emitting diodes are known to vary in wavelengths from unit-to-unit.
Other optical probes are shown in patents to Shaw, U.S. Pat. No. 3,683,640, Neilsen, U.S. Pat. No. 4,167,331, and Konishi, U.S. Pat. No. 3,998,550.